1. Field of the Invention
The present invention is concerned with an illuminated display apparatus. The invention finds particular, although not exclusive, application as a means for back-lighting liquid crystal displays (LCDs).
2. Discussion of the Background Art
Back-illuminated flat panels have typically incorporated either an edge located light batten or a straight fluorescent tube positioned along the length of an edge of the panel. Prior art arrangements of the above type that use linear light sources are disclosed in U.S. Pat. No. 5,219,217 to Aikens and European Patent Publication No. 879991 in the name of Matsushita Electric Industrial Co., Ltd. for example.
Such illuminated panels are characterised by the use of reflective surfaces provided either adjacent to or within the panel, which surfaces are arranged to reflect light from the linear source out through a major surface of the panel towards an observer. Typically reflective surfaces are arranged with an axis parallel to both the linear light source and a major panel surface to maximise reflection of light scattered from the light source. However, such prior art illumination arrangements suffer from the disadvantage that grooves are positioned in the line of sight of the viewer, thus further diffusive stage such as Fresnel lens must be added to the assembly, as for example in European Patent Publication No. 879991.
Back-illuminated flat panels find particular application for back-lighting LCD displays such as find application in lap-top computers, handheld televisions, video camera view-finders and like devices. Such devices are usually battery powered and so it is particularly important that the display consumes a minimum of power.
In order to minimise power consumption prior art designs have incorporated Fresnel lenses into their design thereby maximising visibility of the display from a location perpendicular to the screen. A serious problem with this approach however is that visibility may be critically reduced when the screen is viewed from an off-perpendicular position.